H 2 /Ar Plasma Interactions with a-c:h Surfaces: A Detailed Study of Modified Layer Formation and Erosion

Transcription

1 H 2 /Ar Plasma Interactions with a-c:h Surfaces: A Detailed Study of Modified Layer Formation and Erosion N. Fox-Lyon, F. Weilnboeck, G.S. Oehrlein Department of Material Science and Engineering, Department of Physics, and Institute for Research in Electronics and Applied Physics University of Maryland, College Park, Maryland, N. Ning, D.B. Graves Department of Chemical Engineering, University of California, Berkeley, CA Presented at AVS International Symposium, October 21 st 2010

2 Motivation Plasma modification of amorphous hydrocarbon (a-c:h) Model material Hard mask materials Polymeric materials Fusion plasma facing materials How can we study change in surface properties in real time? Surface topography Chemical composition Depth of modification Can MD simulations reproduce/predict surface properties seen experimentally? Laboratory for Plasma Processing of Materials 2

3 Outline Plasma on a-c:h films Ar plasma H 2 plasma Ar/H 2 plasma Ion energy dependencies Experimental vs. molecular dynamics simulations Laboratory for Plasma Processing of Materials 3

4 Experimental Deposition of a-c:h films: CH 4 plasma 33-35% H 25-30% sp 3 bonds ~80 nm thick on silicon Erosion of a-c:h films: Ar plasma H 2 plasma Ar/H 2 plasma Characterization: In-situ single wavelength ellipsometry X-ray photoelectron spectroscopy Atomic force microscopy Laboratory for Plasma Processing of Materials 4

5 Real-time ellipsometry Real-time ellipsometry used to determine properties during growth of a-c:h films Allows for determining level and depth of modification in real-time Surface topography Chemical composition Density Laboratory for Plasma Processing of Materials 5

6 Deposition followed by erosion using H 2 or Ar Large change in optical density Opposite effects for Ar and H 2 plasmas Laboratory for Plasma Processing of Materials 6

7 Deposition followed by erosion using H 2 or Ar a-c:h H 2 Ar Large change in optical density Not due to roughening <1 nm RMS Laboratory for Plasma Processing of Materials 76

8 Ar plasma on a-c:h Laboratory for Plasma Processing of Materials 87

9 Ar plasma on a-c:h Laboratory for Plasma Processing of Materials 97

10 Ar plasma on a-c:h Exposing surface to Ar ions causes optical densification Real-time ellipsometry measurements also show film densification and loss of hydrogen Laboratory for Plasma Processing of Materials 7 10

11 Ar plasma on a-c:h H depleted layer thickness Exposing surface to Ar ions causes optical densification Real-time ellipsometry measurements also show film densification and loss of hydrogen Laboratory for Plasma Processing of Materials 7 11

12 Ar plasma on a-c:h H depleted layer thickness unmodified a-c:h thickness Exposing surface to Ar ions causes optical densification Real-time ellipsometry measurements also show film densification and loss of hydrogen Laboratory for Plasma Processing of Materials 7 12

13 Ar plasma on a-c:h Exposing surface to Ar ions causes optical densification Real-time ellipsometry measurements also show film densification and loss of hydrogen Laboratory for Plasma Processing of Materials 7 13

14 H 2 plasma on a-c:h 14 Laboratory for Plasma Processing of Materials 8

15 Ellipsometric map of H 2 on a-c:h Ellipsometric map A map of the real-time ellipsometric modeling of the H 2 plasma on a-c:h surfaces can be constructed A polymeric film (~50%H) is simulated on the surface 15 Laboratory for Plasma Processing of Materials 8

16 Ellipsometric map of H 2 on a-c:h Ellipsometric map A map of the real-time ellipsometric modeling of the H 2 plasma on a-c:h surfaces can be constructed A polymeric film (~50%H) is simulated on the surface 16 Laboratory for Plasma Processing of Materials 8

17 Ellipsometric map of H 2 on a-c:h polymeric layer thickness Ellipsometric map A map of the real-time ellipsometric modeling of the H 2 plasma on a-c:h surfaces can be constructed A polymeric film (~50%H) is simulated on the surface Laboratory for Plasma Processing of Materials 8 17

18 Ellipsometric map of H 2 on a-c:h polymeric layer thickness unmodified a-c:h thickness Ellipsometric map A map of the real-time ellipsometric modeling of the H 2 plasma on a-c:h surfaces can be constructed A polymeric film (~50%H) is simulated on the surface Laboratory for Plasma Processing of Materials 8 18

19 H saturated layer formation Hydrogenated layer high bias voltages lead to lower thickness of modified layer Laboratory for Plasma Processing of Materials 9 19

20 H 2 plasma bias/erosion rate effects Hydrogenated layer Lower thicknesses caused by higher erosion rates 20 Laboratory for Plasma Processing of Materials 10

21 Ar/H 2 plasmas on a-c:h 21 Laboratory for Plasma Processing of Materials 11

22 Ar/H 2 plasmas on a-c:h Two opposite surface effects Hydrogen depletion Ar Plasma Hydrogen saturation H 2 plasma What happens when H 2 gas is added to Ar discharge? Do we expect to see loss of densification? Re-population of sites with H? Erosion rate changes? 22 Laboratory for Plasma Processing of Materials 11

23 Ar/H 2 plasmas on a-c:h Surface modification At low hydrogen contents (<5%) the surface densifies like pure Ar At 5% H 2, the surface first densifies then hydrogenates to about 2 nm Higher %H 2 begin to approach pure H 2 in terms of H saturation at the surface 23 Laboratory for Plasma Processing of Materials 11

24 How does experiment compare with MD? a-c:h surface - Ar initial surface Laboratory for Plasma Processing of Materials 24 12

25 How does experiment compare with MD? Hydrogen depleted, dense a-c:h surface - Ar Loss of hydrogen Densification initial surface after 3000 impacts Laboratory for Plasma Processing of Materials 25 12

26 How does experiment compare with MD? Hydrogen depleted, dense a-c:h surface - Ar Loss of hydrogen Densification initial surface Qualitative/Quantitative agreement with experimental results after 3000 Ar impacts Laboratory for Plasma Processing of Materials

27 How does experiment compare with MD? a-c:h surface H 2 Laboratory for Plasma Processing of Materials 27 13

28 How does experiment compare with MD? initial surface a-c:h surface H 2 Laboratory for Plasma Processing of Materials 28 13

29 How does experiment compare with MD? initial surface 1500 H 2 impacts a-c:h surface H 2 Initial increase in thickness due to swelling Laboratory for Plasma Processing of Materials 29 13

30 How does experiment compare with MD? initial surface 1500 H 2 impacts 8000 H 2 impacts a-c:h surface H 2 Initial increase in thickness due to swelling Saturation of hydrogen (to ~50%) steady state layer Laboratory for Plasma Processing of Materials 30 13

31 How does experiment compare with MD? initial surface 1500 H 2 impacts 8000 H 2 impacts a-c:h surface H 2 Initial increase in thickness due to swelling Saturation of hydrogen (to ~50%) steady state layer Thickness - ~2nm vs. 6-8 nm seen experimentally Laboratory for Plasma Processing of Materials 31 13

32 Summary Ar plasma on a-c:h: Dense, hydrogen depleted layer formed Degree of modification increases with ion energy H 2 plasma on a-c:h: Initial surface swelling with hydrogen Steady-state hydrogen saturated layer at the surface Degree of modification shrinks with increasing ER Ar/H 2 plasma on a-c:h: Competition of hydrogen saturation and depletion Can control surface behavior with small plasma chemistry changes MD simulations: Quantitative agreement for Ar plasma on a-c:h Qualitative agreement for H 2 plasma on a-c:h Laboratory for Plasma Processing of Materials

33 Acknowledgements We thank E. Bartis and M. Graves for helpful discussions and contributions to this project. We gratefully acknowledge support of this work by the US Department of Energy Office of Fusion Energy Sciences (DE-SC ) Laboratory for Plasma Processing of Materials